Catalyst preparation



Patented Sept. 20, 1 949 CATALYST PREPARATION Christian J. Wernlund, Niagara Falls, N. Y., as-

signor to E. L-du Pont de Nemours & Company... VViImington, Del., a corporation of Delaware No Drawing. Application February 21, 1947,

Serial No. 730,210

1 Claim.

This invention relates to catalyst preparation and, more particularly, it relates to the production of a catalyst structure comprising manganese dioxide.

It is an object of this invention to produce a new and improved catalyst structure comprising manganese dioxide.

It is another object of this invention to produce a solid catalyst structure comprising an outer coating of manganese dioxide.

It' is still another object of this invention to produce a manganese dioxide catalyst which has particular utility in. the decomposition of hydrogen peroxide.

Other objects of the invention will appear hereinafter.

The objects of this invention may be accomplished, 'in general, by electrodepositing black manganese dioxide on a cathode from an aqueous electrolytic solution containing potassium car bonate, potassium permanganate, and potassium manganate.

The manganese dioxide may be directly electrodeposited on. a metal supporting structure, for example, a supporting structure of iron, steel, nickel, aluminum, or manganese. It is preferred, however, to first electrodeposit manganese on an iron or steel.- support and then electrodeposit manganese dioxide on said support.

In order to obtain-a particularly desirable form of catalyst structure, a foraminous supporting structure ofiron or steel is'used. 'Ih-isstructure may be a section of wire-mesh screen having a mesh size between inch and A; inch: or it may be perforated iron or steel sheeting having a com- Wire-mesh screen of parable size of openings. this type canbe obtained as plain screen without protective coating or as an unlacquered-gal-vanized or. lacquered-galvanized screen. When the screen structure contains no protective coating or when it contains a lacquer coating, it is pref-erablyfirstcleaned with an alkaline-cleaning solu tion', for example, an aqueous solution containing 8 to 16 ounces per gallon of caustic soda. The screen may be cleaned in such solution by immersing it in the solutionhaving a temperatureof 90 C. to 100 C. for a period of ten mi-nutesand- The-screenmay. be immersed in the acid pickling bathafor" a period of three to ten minutes, or as much longeras necessary to remove the galvaniz ing (zinc) therefrom and produce a clean steel".

surface. other acid pickling. bath which will produce. a-cl'ean'steel surface can, of course, be used. 1

The: cleansteel screenxmay next be subjected 1 to plating with m'anganese, or alternatively, manganese dioxide may be el'ectrodeposited directly on the: steel surface. Preferably, the steel supporting structureis first platedwith manganese. This may be done by any known-manganeses plating process; Particularly good results have been obtained by plating-from an aqueous solution containing manganese acetate,

(MHQCHsOz) 2'4H20) ammonium-v acetate, and ammonium hydroxide. Good resultshavealso been obtained by plating from: an'aqneoussolution containing manganese sulfocya'n-ate- MnICNSlz 3H2O) ammonium sulfocyana-te, and-ammonium hydroxide.

Plating-manganese from an acetate solution may be carried out asfollows:

The clean steel supporting structure is made cathode in an aqueous plating bath containing 200 to 300 grams perliter manganese acetate quadrihydrate Mn'(C2I-I 3O2)2'4H20, 150 to 210 grams per liter ammonium acetate and 1.5 to 3.0 grams per'liter ammonium hydroxide. This solution may bemadeup-by dissolving 40 to 65 parts by weight of 'metallicmanganese (electrolytic grad'e) in'Z-ZG- to 300- 'parts by weight of 100% acetieacid and 490- to 600 parts by weight of water. When all the manganesehas-dissolved, add 150 to 200' parts by weight of ammonium hydroxide, and add sufficient more ammonium hydroxide toproduce a pH-"of T to 8.

Theplati-ng is carried out with graphite anodes,

preferablywith cotton bags around the anodes.

The total anode area should be as large as possible; The anode current density is preferably ma-in-tained between and 30 amperes per square foot; and the cathode current density between 60 and 150amperesper square foot, dependingupon' the temperature of the plating bath. If the'plating bath has-a temperature between C. and

- '-C.-a cathode current" density of to amperes per square foot is preferred, and if the bath has a temperature of 40 C. to 50 C. a current density of to amperes per square foot will be preferred. The lower temperature range and lower cathode current density gives the best results. An E. M. F. of 6 to 9 volts is preferred. Plating for one to two hours will produce a desircameos aqueous solution containing 200 to 300 parts by weight of ammonium sulfocyanate and 600 to 1000 parts by weight of water. The mixture is boiled until the manganese is dissolved. The solution should contain about 200 to 250 grams per liter manganese sulfocyanate (Mn(CNS) 2-3H20) about 75 to 125 grams per liter ammonium sulfocyanate and suflicient ammonium hydroxide to produce a pH of between 7.5 and 9.0.

The plating is carried out with graphite anodes at current densities, bath temperatures, and E. M. F. similar to the operating conditions above referred to with reference to plating from a manganese acetate solution. This bath may be replenished by addition of electrolytic manganese and ammonium sulfocyanate as required to maintain the bath contents within the ranges above described. A sufficiently thick deposit will be obtained after one or two hours of plating.

The manganese plated steel structures may be rinsed with water. and the manganese dioxide electrodeposited thereon. .However, if desired, the steel supportin structure may be subjected to electrodeposition of manganese dioxide Without first electrodepositing manganese thereon. It is of advantage to first deposit manganese on the steel because the electrodeposited manganese dioxide is otherwise rapidly removed from the steel supporting structure when used in the decomposition of 27% to 100% H202. manganese is, therefore, highly desirable so that the hydrogen peroxide decomposition reaction can be maintained for extended periods.

The cathodic electrodeposition of manganese dioxide on the steel or the manganese-coated steel is carried out in an aqueous solution containing potassium carbonate, potassium permanganate and potassium manganate. This solution may be produced by first dissolving between 100and 140 grams per liter potassium carbonate and 8130 30 grams per liter potassium permanganate in water,

and reducing the permanganate by passing an electric current through said solution with iron anodes and cathodes for about one to three hours at about ampere hours per gallon. The bath is then ready for cathodic electrodeposition of manganese dioxide on the supporting structure. Sheet steel anodes are employed with an anode current density of 10 to 40 amperes per square foot. Preferably, the bath is maintained at C. to 30 C. Sufficient anode area in the bath to give a ratio of anode area to cathode area of about 2 to 1 is preferred. A cathode current density of to 50 amperes per square foot is desirable. A -minute operation of electrodeposition will produce a satisfactory coating of manganese dioxide. The manganese dioxide will, under the above conditions, be deposited at the An undercoat of 1 4 rate of about 0.04 gram per ampere hour. The bath may be replenished by adding about one pound of KMnO4 for every 1000 ampere hours of operation.

The manganese dioxide catalyst structures produced in accordance with the present invention are particularly useful as decomposition catalysts for hydrogen peroxide solutions containing between 27% and H202 by weight. These catalysts may, however, be used wherever manganese dioxide has a useful function as a catalyst. When use is made of the catalytic structure of the present invention for the decomposition of hydrogen peroxide, it is only necessary to immerse the same in the aqueous peroxide solution.

Reference in the specification and claims to parts, proportions and percentages, unless otherwise specified, refers to parts, proportions and percentages by weight.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited to said details except as set forth in the appended claim.

What is claimed is: r

The process of producing a catalytic structure particularly suitable for. the decomposition of v hydrogen peroxide whichicomprises cathodically electrodepositing manganese on an iron support by plating for aperiodof one to two hours with graphite anodes froman aqueous plating bath containing 200 to 300 grams per liter manganese acetate quadrihydrate, 150 to 210 grams per liter ammonium acetate and 1.5 to 3.0 rams per liter ammonium hydroxide, and then cathodically electrodepositing manganese dioxide on said manganese surface by plating for aperiod of at least 30 minutes with steel anodes from an aqueous electrolytic plating'solution prepared by dissolving 100 to grams per liter potassium carbonate and 8 to 30 grams per liter potassium permanganate in water, and passing an electric current for a period of one to three hours through said solution with iron anodes and cathodes to produce potassium manganate in the solution.

CHRISTIAN J. WERNLUND.

REFERENCES CITED The following references are of record in the file of this patent;

STATES. PATENTS Date OTHER REFERENCES Transactions of 1 the Electrochemical Society, V01. 73, (1938),}313. 327-335, 

